Most high school / middle school tracks have 8 lanes.

The best lane depends on the race.

For races run on the straight away, lanes 4 and 5 are the best, then 3 and 6, then 2 and 7, and then 1 and 8

For races run around curves, the best lanes depend on the runner.  If a runner is very comfortable running around lane 1, then that might be the best for that runner.  That curve is the tightest, and quickest.  Most runners prefer lane 3 or 4, that way (if there are 8 competitors), then can see some in front of them, which gives racers added incentive.  In lane 7 or 8, runners have a gentler curve, but then they can not see the competitors.  If cutting in after 2 turns, they also have to be sure to make a straight line to the opposite curve of the track, rather than suddenly jutting over into lane one, which has the effect of increasing the distance run.

Running close to the line in curves is an advantage.  In fact, the farther out the lane is, the more an advantage it is to run close to the line.  That is because the distance is not measured along the line, but actually about 6 inches in from the line.  So, running closer to the line shortens the race.  The difference is about 1/2 meter per lap.  Remember, stepping on the line for 3 times in a row (such as right-left-right or right-right-right) is a disqualify, which you won't find out about until after you finish the race.

For relays, one lane does have an advantage, depending on which athletes are doing the exchange.  Take a look at the exchange zone for the 100m.  The first exchange for lane 8 is almost all straight.  On the other hand, lane 1 does the entire exchange on the curve, which means they are exchanging more in the middle of the lane, slightly lengthening run.

Another example is the first exchange of the 4x200 relay, which for lane 8 is far around the curve.  Lane 1, it is on the straight for all exchanges.  It would seem that the best lane for the 4x200 would probably be lane 1, 2 or 3.